Microprocessor-based engine controllers are well-known in the art of internal combustion engines. Such devices are used not only to improve performance but to reduce emissions and accurately control engine operations. The advent of microprocessor or computer control of engine operation has opened the door to a panoply of feedback control systems implementing a wide variety of engine control objectives. Examples of such systems are electronically timed ignition systems, digitally controlled fuel injection systems and emission control systems including mass air flow transducers, temperature sensors, pressure sensors and other feedback devices useful in determining emission or pollutant levels in the exhaust system of a vehicle.
In recent years, electronic engine control systems have found applications in the heavy duty engine market, more particularly the diesel engine market. One example of such a system is the CELECT engine control system manufactured by Cummins Engine of Columbus, Ind., and available with their N-14 engine, as well as other engine models. The CELECT electronic engine control system was first introduced in 1990 and has been well received by the heavy duty trucking industry. One of the advantages of a fully electronic engine control system is the ability to modify the software or program to implement newly devised engine control algorithms in response to a recognition of the need for the algorithm. The present invention contemplates an engine control system that implements an algorithm enabling a derated lower power output engine to operate at a higher power output level under certain prescribed conditions or circumstances.
Engine control systems that enable engine operation at more than one maximum power output capability based upon certain operating conditions are known. Examples of such systems are disclosed in U.S. Pat. No. 5,019,986 to Londt et al, U.S. Pat. No. 4,914,597 to Moncelle et al. and U.S. Pat. No. 4,493,303 to Thompson et al. Each of these system limits fuel flow rates, via fuel injection systems, depending upon certain sensed parameters. The Moncelle et al. patent suggests that variable power limits can be established to operate an engine under cruise control conditions to provide more desirable operating characteristics. Unfortunately, large tracts of public roads include road grade deviations sufficient to discourage the use of cruise control with heavy duty trucks in view of the "lug up" and "lug down" characteristics of operating a heavy duty truck. For example, when a heavy duty truck or tractor/trailer combination is operating at 60,000 to 80,000 pounds gross weight, even a small hill or incline will induce a distracting velocity decrease of the truck even though the engine of the truck is operating at full power output. Thus the efficacy of a cruise control system is significantly affected when a heavy duty truck encounters hills or inclines while operating in "cruise" mode.
An engine control system that is more responsive to road grade deviations and enables the truck to maintain a constant speed yet limits power output in such a fashion as to prevent excessive power under lower road load demand conditions will increase driveability of the vehicle as well as reduce certain hardware requirements for the vehicle and reduce Brake Specific Fuel Consumption (lbs/hp-hr) resulting in improved fuel economy. Increased power capability under certain operating conditions also enables the driver to avoid downshifts which can degrade fuel economy. Such an engine control system is needed to improve run times or delivery time, maintain vehicle mileage rates at an acceptable value yet satisfy the driver in terms of vehicle performance characteristics.